1. Field of the Invention
The present invention relates to a manufacturing method provided with a deposition device for depositing materials which can be deposited by evaporation (hereinafter, an evaporation material), and a manufacturing method of a light emitting device that has a layer containing an organic compound as a light emitting layer with the manufacturing apparatus. Specifically, the present invention relates to a vacuum-evaporation method and an evaporation apparatus that conducts deposition by evaporating an evaporation material from a plurality of evaporation sources provided to face a substrate.
2. Description of the Related Arts
In recent years, a research related to a light emitting device having an EL element as a self-luminous light emitting element has been activated. The light emitting device is referred to as EL display or light emitting diode (LED). Since these light emitting devices have characteristics such as rapid speed of response that is suitable for movie display, low voltage, low power consumption driving, or the like, they attracts an attention for a next generation display including new generation's cellular phones and portable information terminals (PDA).
An EL element that has a layer containing an organic compound as a light emitting layer has a structure that an organic compound-containing layer (hereinafter, an EL layer) is sandwiched between an anode and a cathode. Electro luminescence is generated in the EL layer by applying an electronic field to the anode and the cathode. Luminescence obtained from the EL element includes light emission in returning to a base state from singlet excitation (fluorescence) and light emission in returning to a base state from triplet excitation (phosphorescence).
Above EL layer has a laminated structure typified by “a hole transporting layer, a light emitting layer, an electron transporting layer”. An EL material for forming an EL layer is classified broadly into a low-molecular (monomer) material and high-molecular (polymer) material. The low-molecular material is deposited using the evaporation apparatus.
The evaporation apparatus has a substrate holder installed on a substrate, a melting pot encapsulated an EL material, an evaporation material, a shutter for prevention of rising an EL material that will be sublimed, and a heater for heating an EL material in a melting pot. Then, an EL material heated by the heater is sublimed and deposited on a rolling substrate. At this time, in order to deposit uniformly, the substrate and the melting pot is necessary to have a distance therebetween at least 1 m.
According to the above-described evaporation apparatus and the above-described vacuum evaporation method, when the EL layer is formed by vacuum evaporation, almost all of the sublimated EL material is adhered to an inner wall, a shutter or an adherence preventive shield (protective plate for preventing a vacuum evaporation material from adhering to an inner wall of a deposition chamber) at inside of the deposition chamber of the evaporation apparatus. Therefore, in forming the EL layer, an efficiency of utilizing the expensive EL material is as extremely low as about 1% or smaller and fabricating cost of a light emitting device becomes very expensive.
Further, according to the evaporation apparatus of the related art, in order to provide a uniform film, it is necessary to separate a substrate from an evaporation source by an interval equal to or larger than 1 m. Therefore, the evaporation apparatus per se becomes large-sized, a time period required for emptying gas from each deposition chamber of the evaporation apparatus is prolonged and therefore, a deposition rate is retarded and throughput is lowered. Moreover, when the substrate becomes larger, there is the problem that the film thickness of the center part and the margin of the substrate easily become different. Further, the evaporation apparatus is of a structure of rotating the substrate and therefore, there is a limit in the evaporation apparatus aiming at a large area substrate.
Further, the EL material poses a problem of being deteriorated by being easily oxidized by presence of oxygen or water. However, in forming a film by an evaporation method, a predetermined amount of an evaporation material put into a vessel (glass bottle) is taken out and transferred to a vessel (representatively, crucible, or evaporation boat) installed at a position opposed to an object to be formed with a film at inside of an evaporation apparatus stem and there is a concern that the evaporation material is mixed with oxygen or water or an impurity in the transferring operation.
Further, when the evaporation material is transferred from the glass bottle to the vessel, the evaporation material is transferred by the human hand at inside of a pretreatment chamber of a deposition chamber provided with a glove or the like. However, when the glove is provided at the pretreatment chamber, vacuum cannot be constituted, the operation is carried out under atmospheric pressure and there is a high possibility of mixing an impurity. For example, even when the transferring operation is carried out at inside of the pretreatment chamber subjected under a nitrogen atmosphere, it is difficult to reduce moisture or oxygen as less as possible. Further, although it is conceivable to use a robot, since the evaporation material is in a powder-like shape, it is very difficult to fabricate the robot for carrying out the transferring operation. Therefore, it is difficult to constitute steps of forming an EL element, that is, from a step of forming an EL layer above a lower electrode to a step of forming an upper electrode by an integrated closed system enabling to avoid mixing of an impurity.